Aluminum Curtain Wall Installation Details

Factory Modules, Anchors, Mullions and On-Site Assembly Logic

Aluminum curtain wall systems are not just “glass and profiles”. Behind every façade, there is a precise installation logic that starts in the factory with cutting and machining, continues with accurate anchor placement on site, and is completed with mullion–transom assembly, glass installation and final capping. In this guide, we examine the main installation types of stick curtain wall systems, anchor strategies and load paths in detail.

1. Factory Production: Left and Right Modules

In the illustration, the left and right vertical frames are produced in the factory as ready-made modules. The following elements are processed in the factory:

• Mullion (vertical member) cuts
• Grooves for the seating of transoms (horizontal members)
• EPDM gasket channels
• Connection shoes (brackets) mounted on profile ends where required
• Holes, slots and dimensional tolerances

In this way, error-prone on-site operations such as cutting, drilling and dimensional adjustment are minimised.

2. Pre-Fixed Anchors

The anchors fixed to the concrete slab are clearly visible in the upper part of the illustration. The logic here is:

• All façade lines are kept on the same axis using a laser.
• Anchors are adjusted with ±2–3 mm tolerance to match the module seating dimensions.
• The tension, shear and moment capacities of each anchor are determined according to structural calculations.

This step ensures that the entire installation is built correctly from the “skeleton” upwards.

3. On-Site Installation Sequence (Flow Explained by the Illustration)

3.1 First Module (Left Frame) Seated on Anchors

The module is slid towards the anchors in the direction indicated by the arrows and locked. The mullions seat into the slots on the anchors. The aim here is:

• To connect the module to the primary support structure in a single operation
• To ensure exact alignment and plumb in the vertical axis
• To create a reference for the upper modules

3.2 Transoms Installed Between the Modules

The horizontal profiles seen between the two modules are assembled on site. Their functions are:

• Form the horizontal support line for the glass
• Distribute wind suction and pressure loads across the surface
• Guide the fire barrier and insulation system

Technical checks at this stage:

• Deflection and bending tolerances of the transoms
• EPDM insulation gaskets installed before assembly
• Alignment of condensate channels

3.3 Right-Hand Module Installed

The right-hand module is also seated on the anchors in the same way and locked to the transoms. This element:

• Completes the stiffness of the frame
• Closes the single-unit module logic
• Creates the reference for the next vertical module

4. Glass Installation

Once the structural frame is fully assembled:

• Glass setting blocks are placed on the bottom transom
• IGU units are positioned inside the module using a vacuum lifter
• Glass–aluminum contact surfaces are checked
• Continuity of vertical and horizontal gaskets is ensured

The most critical point at this stage: the glass load must be transferred only onto the glass setting blocks, not directly onto the aluminum profile.

5. Closing the System (Capped or Silicone Curtain Wall)

Two different applications are possible depending on the system type.

5.1 Capped Curtain Wall Systems

• Pressure plate screws are tightened
• External cover caps are installed
• The cap lines are checked in both horizontal and vertical directions

5.2 Silicone Curtain Wall Systems

• Silicone gaskets are compressed
• Silicone joints are left between the exterior glass edges
• Structural silicone is applied according to the manufacturer’s datasheet

5.3 Core Logic of This Installation Type

The illustration explains the following idea: “To reduce on-site workload, all vertical elements are prepared in the factory as modules, and the façade frame is created on site simply by locking these modules together.”

Main advantages:

• Reduced error margin
• Increased installation speed
• Quality control is moved to the factory
• On-site workmanship standard is improved

This method is highly efficient especially in:

• High-rise buildings
• Façades with repetitive modules
• Projects with tight mullion spacing

6. Aluminum Curtain Wall Systems – Factory-Cut, Site-Assembled Type

This installation type is where aluminum profiles are only cut, drilled, slotted and machined for brackets in the production line, but not assembled as modules, and then joined together on site. It is the purest and most common form of the stick system.

6.1 Factory Preparation Process

This method offers major advantages in the production–supply chain. Operations carried out in the factory:

• Profiles are cut to exact lengths
• Slots and recesses for seating transoms are machined
• Bracket recesses for anchor connections on mullions are prepared
• Hole locations are processed with CNC according to coordinates
• Condensate channels and EPDM gasket grooves are prepared

Thus, error-free, correctly cut pieces arrive on site; all that remains is assembly.

6.2 Installation of Structural Anchors on Site

L-shaped anchors placed under the concrete slab transfer structural loads. Their functions:

• Transfer wind and vertical loads to the reinforced concrete structure
• Support the mullions in the vertical plane
• Establish the axis and plumb line of the façade

This stage is the primary “skeleton” reference of the entire façade system.

6.3 Connection of Mullions to Anchors

Two vertical rows of mullions are installed by:

• First seating on the lower anchors
• Then fixing with the upper anchors
• Aligning for plumb and axis using adjustment screws

The stand-off distance between mullion and anchor requires tolerances up to ±5 mm. If this adjustment is not done, glass openings shift, panels do not fit and the façade grid is distorted.

6.4 Installation of Transoms Between Mullions

The transoms:

• Are cut to exact length in the factory
• Are installed between two mullions on site
• Are usually fixed with “fish-mouth” or T-slot type connections
• Receive their EPDM gaskets afterwards

They:

• Create the horizontal support line carrying the glass
• Transfer the structural load to the mullions
• Allow condensate water to be drained

Therefore, transoms must not bend or twist and must sit exactly on their axis.

6.5 System Working Principle

The backbone of this system is: “All profiles are prepared in the factory, all assembly is done on site.”

Advantages:

• No need to produce full modules
• Profiles can be supplied more quickly
• Dimensions can be corrected on site if needed
• Cost is lower than modular systems

Disadvantages:

• More on-site labour and time
• Higher error margin compared to modular systems
• Longer installation time on very tall buildings

In Türkiye, the Middle East and the Balkans, this is still the most widely used method because it is flexible, economical and continuously adaptable.

6.6 Glass and Exterior Surface Installation

1. Glass setting blocks are placed.
2. Glass units are installed with a vacuum lifter.
3. Pressure plates and caps are mounted.
4. In silicone curtain walls, exterior joints between glass panes are filled.

At this stage, the façade becomes an envelope that provides air and water tightness.

7. Mullion Installation from Floor to Slab (Full-Height Mullion)

This step explains installing mullions from floor to slab in a single length. This is the fundamental step in all stick, capped, silicone and modular stick curtain wall systems.

We clearly see:

• Lower anchor fixed to the slab
• Upper anchor fixed to the slab above
• A single full-height mullion fixed between them
• Critical connections for plumb, axis and load transfer

7.1 Function of the Bottom Anchor

The bottom anchor:

• Determines the vertical axis where the mullion will be positioned
• Resists shear forces due to wind pressure
• Acts as the starting point that keeps the profile standing

The anchor must be positioned on the reinforced concrete slab according to structural design; if placed incorrectly, the entire façade line will shift.

7.2 Top Anchor – Main Carrier of Structural Load

The top anchor typically:

• Carries vertical loads from the glass weight
• Resists wind loads
• Controls the horizontal movement of the mullion
• May include a sliding slot to allow for thermal expansion

Its installation must be checked with a laser, deviation must not exceed ±2–3 mm, and plumb must be precise.

7.3 “Single-Piece Mullion” Logic

This method provides:

• Increased stiffness with fewer joints and error points
• Perfect plumb line with no misalignment at splice joints
• Straight silicone and cap lines
• Healthier load distribution directly to the anchors

7.4 Installation Sequence on Site

1. Façade axes are marked using laser and string lines.
2. Bottom anchors are fixed to the slab.
3. Top anchors are positioned according to dimensions.
4. The mullion is seated on the bottom anchor.
5. It is lifted to and fixed at the top anchor.
6. Plumb, axis, spacing and verticality are adjusted.
7. The system is made ready for transom installation.

Once this step is completed, the façade has formed its initial structural skeleton.

7.5 System Logic – Load Path

The installation philosophy can be summarised as:

“Load from the glass → mullion → anchor → reinforced concrete slab.”

Therefore, the mullion:

• Must not twist
• Must not deviate from its axis
• Must have full contact with top and bottom anchors
• Must allow for thermal expansion

7.6 Educational Message

For students and site teams, this illustrates that: “Façade installation starts with the mullion; the entire system is shaped according to this line.”

Transoms, glass, caps and silicone joints all depend on the accuracy of this first step.

8. Mullion Fixing Types (Both Compatible with Movement Joints)

Two different techniques are used to connect mullions to anchors. Both are compatible with movement joint solutions and both are structurally correct. The choice depends on site access conditions, architectural appearance, anchor position and mullion layout.

8.1 Left Connection – Side-Fixed Anchor (Standard and Most Common)

In this method:

• The anchor is connected to the side of the mullion.
• The connection plate works from the side of the profile.
• The mullion is given the necessary allowance for thermal expansion and building movement.

It is easy to access, fast to adjust, practical for alignment and standard in most capped and silicone curtain walls. Sliding slots used in the mullion or connection absorb thermal expansion and building drift.

8.2 Right Connection – Top-Fixed, Center-Axis Mounting

In this method:

• The anchor plate is placed under the slab.
• The profile sits on and is fixed to the anchor from above.
• The connection is made along the exact center axis of the mullion.

Preferred when:

• Side connections should not be visible in the architectural line.
• The anchor must work from the exact center axis of a grid.
• Transoms must align with the center axis.
• Top-seated solutions are used in steel–aluminum hybrid structures.

Even though the profile is fixed from above, movement at the bottom connection allows for thermal expansion and building movements.

8.3 Summary

Both connection types are suitable for movement joint solutions. The difference is not in movement capacity but in installation approach and architectural preference.

9. Floor-by-Floor Anchoring (Each Floor Works Independently)

In this method, mullions are anchored separately to each floor slab and do not continue as a single continuous element from bottom to top. This is known as the “floor-independent working principle”.

• Each floor slab receives its own anchors at the top and bottom.
• Mullions are manufactured to floor height.
• The mullion on the upper floor is not structurally continuous with the one below.
• Each floor absorbs its own movements independently.

This is especially preferred in high-rise buildings and seismic regions.

9.1 Core Logic: Floors Work Independently

Buildings sway during earthquakes, experience interstory drift, settlement and micro-movements, and thermal deformations in concrete. If mullions were continuous and locked floors together:

• Glass would crack.
• Profiles would buckle.
• Silicone joints would be overstressed.
• Cap lines would distort.
• Anchors would be overstressed in shear.

By making each floor’s mullion independent, these movements are not transferred directly between floors.

9.2 Technical Advantages

• Improved seismic safety.
• More controlled thermal expansion with shorter mullions.
• Easier maintenance and glass replacement.
• Greater tolerance of dimensional deviations between floors.

9.3 Connection Logic

Each mullion:

• Is fixed at its bottom end to the lower floor anchor.
• Is fixed at its top end to the upper floor anchor.

These connections:

• Carry vertical loads.
• Transfer wind loads to the slab.
• Protect the mullion in horizontal displacement scenarios.

The joint between floors is not structurally locked; it is typically covered architecturally (shadowbox, cap, silicone joint, box profile, railing line, etc.).

9.4 When This System Is Used

• High-rise buildings.
• Buildings in seismic regions.
• Mixed-use residential + commercial buildings.
• New structures with expected concrete settlement.
• Projects where floor slabs work in different directions.

If using a continuous mullion would create risk, working with floor modules is the most appropriate solution.

10. Continuous Mullion System (Sliding Bottom Anchor + Fixed Top Anchor)

Here, two anchor types explain one concept: the bottom anchor is vertically movable, the top anchor is a fixed reference point. Together they allow the mullion to work as a single continuous element along the entire building height.

10.1 Bottom Anchor – Sliding Base Plate

The bottom anchor:

• Is sliding in the vertical direction.
• Allows the mullion to move up and down on the anchor.
• Is solved with slotted holes or double-hole sliding plates.

Movement is necessary because of:

• Thermal expansion: for 6–12 m mullions, seasonal expansion can reach 8–15 mm and must be absorbed at the bottom connection.
• Building settlement: most settlement occurs at base levels; if movement is not allowed, glass can break, cap lines can shift and silicone joints can tear.
• When the mullion is fixed at the top and works rigidly upwards, the bottom must be free to move.

10.2 Top Anchor – Fixed Point Connection

The top anchor:

• Uses slotted or fixed-point holes.
• Connects the mullion rigidly to the structure.
• Creates a “fixed point” that acts as the starting point of the load path.

Its roles:

• Carry glass and mullion self-weight.
• Transfer wind suction and pressure to the structure.
• Keep the façade aligned on the same axis across floors.

10.3 Structural Logic

With this anchor combination, the mullion becomes:

• Fixed at the top.
• Sliding at the bottom.
• Fixed or controlled-slotted at intermediate floors.
• A single continuous vertical structural member transferring loads to the fixed point.

In other words, the system does not work floor by floor; it behaves like a single bar along the entire building height. This is widely used where high stiffness is required.

10.4 When This Method Is Used

• High-performance curtain wall systems.
• Silicone curtain walls.
• Box-type façades.
• Projects where cap lines must be perfectly straight.
• High-rise buildings.
• Buildings in seismic regions where fixed-point control is desired.
• Façades with continuous architectural modules.

11. Anchor Installation System (Step-by-Step Application Guide)

The last illustration explains how to install an anchor on a reinforced concrete surface in six stages. Each step is critical in terms of both structural safety and installation accuracy.

11.1 Stage 1 – Drilling the Concrete Surface

A hole is drilled into the concrete with a drill bit matching the anchor diameter. Hole depth is determined by the embedment depth of the anchor.

Points to consider:

• The hole must be perpendicular to the surface.
• Concrete strength should be at least C25.
• No cracks should form around the hole edges.

11.2 Stage 2 – Cleaning the Hole

The inside of the hole is cleaned using a cleaning pump or compressed air. If dust remains:

• The anchor can pull out.
• Bond strength is reduced.
• Tension and shear capacities decrease.

Correct cleaning → correct load capacity.

11.3 Stage 3 – Placing the Anchor

Two types of anchors can be used:

• Steel expansion anchor (mechanical).
• Chemical capsule (injection anchor).

Selection criteria:

• Required load capacity.
• Concrete class.
• Façade weight.
• Wind pressure.
• Shear and tension demands.

11.4 Stage 4 – Fixing Anchor Rods and Preparing the Plate

Steel rods are placed into the anchors and the base plate that will sit on them is prepared. At this stage:

• The anchor integrates with the concrete.
• The primary load path is formed.
• The fixing plate is positioned.

Plate holes are often slotted to ease alignment.

11.5 Stage 5 – Tightening the Plate with Nuts

The plate is placed over the anchors, washers are fitted and nuts are tightened to the specified torque.

If over-tightened:

• Hole deformation occurs.
• The plate can bend.
• The anchor capacity is reduced.

If under-tightened:

• Loosening under wind loads.
• Mullion movement.
• Loss of system integrity.

Correct torque → correct load transfer.

11.6 Stage 6 – Seating the Mullion on the Anchor

Finally, the mullion (vertical aluminum profile) is seated on the anchor, fixed through the holes in the plate and installation is completed.

At this point, the system:

• Can carry wind loads.
• Is ready for glass installation.
• Is ready for cap/silicone applications.